1. 4 Important characteristics of
Populations
• 1.
GEOGRAPHICAL
DISTRIBUTION
– Area that is inhabited
by a population
• Varies in size
from a few cm3
(bacteria) to
millions of square
kilometers
2. 2. Density of Area
• # of individuals per
unit area
• Ex: desert cactus =
low density
• Cactus brush = high
density
3. Partner activity: Density & Growth
Rate
• Density formula = # of indiv/area
• 1. What is the density of 150 bullfrogs in
a pond that covers an area of 3 sq.
km?
50 bullfrogs/sq. km
4. Growth Rate
• Pf - Pi = Growth Rate **can be a neg.
∆Time number
1. In 1940, 4,800 sea otters were counted in a field
study off the coast of Monterey, Calif. The field
study continued until 1945 when scientists counted
only 2,200 sea otters. What was the growth rate of
sea otters?
2. -520 sea otters/year
5. More Problems
• In the Fall of 2000, there were 1857
students at RAHS. This fall in 2008 the
student count was 2,164. Growth rate?
• 38 students/year
6. 3. Growth Rate (factors that affect
populations
• 1. Number of births
(natality)
• 2. Number of deaths
(mortality)
7. 4. # of members that enter or leave
the population
• Immigration =
movement of
individuals into an
area
• Emigration =
movement of
individuals out of an
area
8. Limiting Factors (affecting
Populations Growth)
• Competition for
• water
• shelter
• food
• Predation
• Parasitism & disease
• Drought & climate
change
• Human disturbances
11. Exponential
Growth (J-
curve)
EXPONENTIAL PHASE
LAG PHASE
12. Exponential Growth
• Occurs when a population reproduces
at a constant rate.
• At 1st, growth is slow
• Under ideal conditions with unlimited
resources, pop. will grow exponentially
13. • Example: bacteria
Partner Activity – Within 20 min.
bacteria will divide &
reproduce asexually
– If an area starts with
2 bacteria cells on it,
how many bacteria
will have grown in 3
hours?
ANSWER = 1024
15. Logistic Growth
• As a resource becomes less available, populations
slows or stops
CARRYING CAPACITY
EXPONENTIAL PHASE
STABILIZATION PHASE
LAG PHASE
